NO145680B - ETHYLENE HOMO AND COPOLYMERIZATION CATALYSTS CONTAINING CHROME, TITAN AND ANY FLUOR, AND PROCEDURES FOR PREPARING THEREOF. - Google Patents

Description

The present invention relates to ethylene homo- and copolymerization catalysts which contain chromium and titanium and also possibly fluorine, as well as a method for producing these catalysts.

Ethylene polymerization catalysts containing chromium and titanium are known. These catalysts represent an improvement in relation to the known earlier catalysts which contained only chromium in that they gave ethylene polymers with a lower molecular weight and which were easier to process than the polyethylenes with a higher molecular weight. Various patents describe specific methods for producing titanium-modified chromium catalysts for ethylene polymerization. US patent no. 3,349,067 describes a method for producing a polymerization catalyst comprising bringing a support material into contact with a solution of a chromium-containing compound in an anhydrous organic solvent. In this description, a reaction in the presence of silicon oxide of chromyl chloride (Cro 2 Cl 2 ) and tetra(n-butyl) titanate is indicated, which produces a precipitate containing titanium and chromium on the silicon oxide support. Such a method therefore depends on the reaction product of chromyl chloride and the organic titanate to deposit on the substrate in a non-unique way.

US patent no. 3,622,521 describes a catalyst which is formed by first adding to a support a chromium-containing compound using an aqueous medium and then adding a titanium-containing compound using a non-aqueous medium. Such a method involves the use of two different solvents and thus involves two separate and distinct deposition steps. Such a process is cumbersome and leads to non-reproducible catalysts for ethylene polymerization.

US Patent No. 3,879,362 relates to a process for polymerizing ethylene using a catalyst prepared by (1) heating a titanium compound and a support material selected from silicon dioxide, alumina, zirconium oxide, thorium oxide or mixtures thereof, and (2) to heating the product from step 1 with a chromium compound at a temperature in the range of 350-550°C to obtain an active catalyst. A number of chromium compounds are indicated in the description including biscyclopentadienylchromium, i.e. chromocene. The main focus is on this two-step process involving either chromium oxide or a tertiary butyl chromate as the source of the chromium compound.

All of the above methods for producing these modified catalysts can cause problems. The catalysts are sensitive to the manufacturing methods and can thus produce polyethylenes that can vary in polymer properties with regard to molecular weight, molecular weight distribution and density. Catalyst activity also varies depending on the way in which the catalyst is produced.

The object of the invention is therefore to produce a catalyst for ethylene polymerization which is easy to manufacture and which shows sufficient catalytic activity. Other items for the invention will be apparent to the person skilled in the art from the following description.

According to the invention, ethylene homo- and -copolymerization catalysts containing chromium and titanium, possibly also fluorine, are thus produced on a carrier which consists of an inorganic oxide which

(a) has high surface area and

(b) is selected from alumina, thorium oxide, silicon oxide, zirconium oxide and mixtures thereof, and

(c) is dried at a temperature of 100-800°C, and

this catalyst is characterized by the fact that it is produced in the following steps:

(1) slurrying dried support with a substantially anhydrous liquid hydrocarbon; (2) mixing the slurry obtained in step (1) with a solution of a chromocene compound of formula

wherein each of Y and Y<1> is a hydrocarbon residue of 1-20 carbon atoms and each of n and n<1> has a value of 0-5, in a liquid hydrocarbon and a titanium compound which is soluble in hydrocarbon and is calcinable to TiO 2 , whereby the resulting mixture apart

from hydrocarbon containing 0.02 to 3.0 wt% elemental chromium and 1.0 to 10 wt% elemental titanium; (3) removing the hydrocarbon to obtain a solid residue; (4) heating the product from step (3) in a substantially anhydrous oxygen-containing atmosphere at a temperature of 30 0 to 1000°C until an active catalyst is obtained.

The invention also relates to a method for producing a catalyst of the above-mentioned type and this method is characterized by the following steps: (1) slurrying dried carrier with an essentially water-free, liquid hydrocarbon; (2) mixing the slurry obtained in step (1) with a solution of a chromocene compound of formula wherein each of Y and Y<1> is a hydrocarbon residue of 1 to 20 carbon atoms and each of n and n' has a value of 0 to 5 in..a liquid hydrocarbon and a titanium compound which is soluble in hydrocarbon and is calcinable to TiC ^, wherein the resulting mixture, exclusive of hydrocarbon, contains 0.02 to 3.0% by weight elemental chromium and 1.0 to 10% by weight elemental titanium; (3a) removing the hydrocarbon to obtain a solid residue; (3b) optional fluoridation with up to 5% by weight of a fluoridating agent, calculated as F; (4) heating the product from step (3) in a substantially anhydrous oxygen-containing atmosphere at a temperature of 30 0 to 1000°C until an active catalyst is obtained.

In the present description, as mentioned, the chromocene compounds, also indicated as bis(cyclopentadienyl) chromium (II) compounds, have the structure:

wherein each of Y and Y' is a hydrocarbon residue of 1 to 20 carbon atoms and each n and n<1> has a value from 0 to 5.

While the mixture of chromocene compound and carrier in step (3) may contain from 0.02 to 3% by weight of chromium, it is preferred to use mixtures containing 0.1 to 1.0% by weight of chromium.

The titanium compound that can be used includes all of them

which are calcinable to TiO 2 under the activation conditions used, and include those described in e.g. US Patent No. 3,622,521. These compounds include those that have the structures

(I) (R') «Ti(OR')

n.m

(II) (RO) Ti(OR') „

m n

wherein m is 1, 2, 3 or 4; n" is 0, 1, 2 or 3 and m + n" = 4,

where R is a C1 to C12 alkyl, aryl or cycloalkyl group and combinations thereof such as aralkyl or alkaryl,

R' is R, cyclopentadienyl, and C2 to C12 alkenyl groups such as ethenyl, propenyl, isopropenyl or butenyl and (III) TiX4 where X, a halogen atom, is fluorine, chlorine, bromine or iodine.

The titanium compounds will thus include titanium tetrachloride, tetraisopropyl titanate and tetrabutyl titanate. The titanium compounds are conveniently deposited on the support from a solution in a hydrocarbon solvent.

In the case of the organic titanates, there is no clear mutual influence between the titanium compound and the chromocene. The deposition of both titanium and chromium compound is believed to occur by direct reaction with the substrate to give chemically anchored titanium and chromium. Such a route to the supported catalysts allows maximum efficiency of the titanium and chromium compounds and allows much better control of the catalyst preparation than the method described in US patent 3,349,067.

Titanium (as Ti) is present in the catalyst with respect to chromium (as Cr), in a molar ratio of 0.5 to 180, preferably 4 to 35.

While the mixture in step (2) can contain from approx. 1.0 to 10% by weight titanium, it is preferred to prepare a mixture containing 3 to 7%, calculated on the weight of the dried mixture.

It is not necessary to include a fluoridating agent. However, fluoridation has the advantage that it gives a narrower molecular weight distribution and better copolymerization of α-olefins. While up to 5% by weight of fluoridating agent can be used, it is preferred that 0.05 to 1.0% is used, calculated as F .

The fluoridating compound which can be used comprises HF or any fluorine compound which gives HF under the activation conditions used. Fluorine compounds other than HF that can be used are e.g. ammonium hexafluorophosphate, ammonium hexafluorosilicate, ammonium tetrafluoroborate and ammonium hexafluorotitanate. The fluorine compounds are suitably deposited on the carrier from an aqueous solution thereof, or by dry mixing of the solid fluorine compound with the other components of the catalyst before activation. The inorganic oxide materials that can be used as carriers in the catalysts according to the present invention are porous substances with a high surface area, i.e. a surface area that lies within the range of 50 to 1000 m 2 per grams, and a particle size of 50 to 200 ym. The inorganic oxides which may be used include silicon dioxide, aluminum oxide, thorium oxide, zirconium oxide and mixtures thereof.

The liquid hydrocarbons can be aliphatic with 5-10 carbon atoms or aromatic with 6-10 carbon atoms. Preferred are isopentane, hexane, benzene, toluene and xylene.

The carrier should be dried before contacting the chromocene and titanium compounds. This usually occurs by simple heating or drying of the catalyst support with a dry inert gas or dry air before use. It has been found that the temperature during drying has a significant effect on the molecular weight distribution and on the melt index of the produced polymer. The preferred drying temperature is 100 to 300°C, while temperatures between 120 and 250°C are most preferred. Activation of the catalyst can be achieved at almost any temperature up to the sintering temperature. Passing a stream of dry air or oxygen through the supported catalyst during activation supports the expulsion of water from the support. Activation temperatures from 300 to 900°C for short periods of 6 hours or thereabouts are sufficient if well-dried air or oxygen is used, and the temperature is not allowed to rise so far that sintering of the support occurs. A preferred activation temperature is approx. 300 to 800°C.

Carrier qualities with a high surface area, and microspheroidal silicon dioxide particles with medium density (MSID) and with a surface area of 300 m 2/gram and a pore diameter of approx. 200 Å, but average particle size of approx. 70 ym, as well as silicon dioxide with medium density (ID), a surface area of approx. 300 m 2 /gram, a pore diameter of approx. 160 Å and an average particle size of approx. 103 ym is preferred.

When it is desired to produce ethylene polymers with a higher melting index, silicon oxides with a pore volume of approx.

2.5 cm 3 /g and a surface area of approx. 400 m2/gram.

The invention shall be described in more detail in the following examples where all parts and percentages are by weight unless otherwise stated.

Example 1. Catalyst preparation.

A "G-952-200" microspheroid silica of medium density, with a surface area of approx. 300 m 2/gram and a pore diameter of approx. 200 Å was dried at 200°C for 8 hours. The dried silica (481 g) was stirred with dry isopentane and 5.3 g of unsubstituted bis(cyclopentadienyl)chromium II (chromocene) and then 168 g of tetraisopropyl titanate was added. Isopentane was removed by evaporation and a dry residue was obtained consisting of 1.1% by weight of chromocene and 35% by weight of tetraisopropyl titanate which were deposited together on the silicon dioxide carrier. The residue was activated by heating for 2 hours under nitrogen at 150 oC

and then 2 hours at 300°C. The nitrogen atmosphere was replaced by air and the heating continued at 300°C for 2 hours. Finally, the temperature was raised to 800°C and held there for 8 hours. Example 2. Catalyst preparation.

The method described in example 1 was followed with the following differences: (1) The amount of silicon dioxide used was 400 g; (2) the amount of bis(cyclopentadienyl) chromium (II) used was 4.4 g; (3) the amount of tetraisopropyl titanate used was 140 g; and (4) the residue, prior to activation, was treated with 1.2 g of ammonium hexafluorosilicate to effect a deposit of 0.3% by weight on the support.

Example 3. Catalyst evaluation.

The catalyst prepared in example 1 was evaluated in a fluidized bed reactor with a diameter of approx. 3 65 mm (corresponding to that described in GB-PS 1,253,063) at 84°C and a reactor pressure of 21 kg/cm 2 gauge pressure with a butene/ethylene mixture present in a ratio of 0.083. The catalyst productivity was 5.3 g/(gram Cr x 10~6). The ethylene-butene copolymer product had a density according to ASTM D-1505 of 0.914 g/cm<3> and a melt index according to ASTM D-1238 of 0.87 dg/min.

Example 4. Catalyst evaluation.

The same procedure as in Example 3 was used to evaluate the catalyst prepared in Example 2 except that the butene/ethylene ratio was 0.084. The catalyst productivity was 4.9 g/(gram Cr x 10~6). The ethylene/butene polymer had a density of 0.9-20 g/cm 3 and a melt index of 0.17 dg/min.

Example 5. Catalyst preparation.

The procedure described in Example 1 was modified in that 7 ml of a toluene solution containing 0.35 g of bis(cyclopentadienyl)chromium II was added to an n-pentane slurry of 19.8 g of "952" silica which had been dried at 200°C, and stirred under nitrogen for one hour after which 6.0 g of tetraisopropyl titanate was added. Pentane and toluene were evaporated and the residue was activated by heating in oxygen at 300°C for 2 hours and at 720°C for 17 hours.

Example 6. Catalyst preparation.

18.6 g of "952" silica, dried at 200°C was slurried in n-pentane and 0.34 g of bis(cyclopentadienyl)chromium II was added to the slurry. After stirring for 1 hour, 5.6 g of tetraisopropyl titanate was added. The n-pentane was evaporated and the residue mixed with 0.19 g of ammonium hexafluorosilicate. The residue was activated by heating in oxygen for 4 hours at 3 30°C and 17 hours at 7 80°C.

E xample 7. Catalyst evaluation.

A high-pressure reaction vessel with a stirrer and a reactor volume of 1000 ml was charged with 0.43 g of the catalyst prepared in Example 5 and 40 ml of 1-hexene. The container

was sealed and pressurized with ethylene to a pressure of

14 kg/cm 2 manometer pressure. The polymerization was carried out at 86°C for 12 minutes. A yield of 78 grams of ethylene polymer was obtained at a melt index of 147 dg/min. and a density of 0.9 22 g/cm<3>.

In a second experiment which differed from the one described above only in that 0.31 g of catalyst was used, and in that the polymerization time was 15 minutes, an ethylene polymer yield of 86 grams was obtained with a melt index of 166 dg/ my. and a density of 0.917 g/cm 3.

Example 8. Catalyst evaluation.

Example 7 was repeated twice using 0.35 g and 0.32 g of catalyst prepared according to example 6 and with polymerization times of 30 and 30, respectively. 20 minutes. Ethylene polymers were obtained in yields of 120 or 56 grams. The melting indices were 0.32 dg/min. respectively 0.64 dg/min. and the density was 0.918 g/cm<3> respectively. 0.917 g/cm<3>.

The catalysts according to the invention were also compared with catalysts according to US patent no. 3,879,362.

Control A: Polymerization of ethylene using a known catalyst.

An ethylene polymerization catalyst was prepared by the technique described in US Patent No. 3,879,362 as follows.

A portion of "952" silica support was dried at 200°C. Then 14.9 grams of the dried silica was slurried in dry pentane and mixed with 4.5 grams of tetraisopropyl titanate. Pentane was removed by evaporation and the residue activated at 780°C for 16 hours in an oxygen stream. A slurry of 15.6 grams of this activated residue was prepared in pentane to which 0.27 grams of chromocene was added. Pentane was removed by evaporation, the residue briefly heated under nitrogen to remove the last traces of pentane and the residue then activated at 810°C for 16 hours in an oxygen stream. The activated residue was used as a polymerization catalyst to polymerize ethylene in a stirred autoclave using hexane as diluent. A polymerization temperature of 90°C was used at a total pressure of 14 kg/cm 2 manometer pressure for 1 hour. Similar experiments yielded polyethylenes with flow indices of 2.8 and 2.4, measured according to ASTM 1238 at 10 times the weight used for the melt index determinations at 190°C.

Example 9: Polymerization of ethylene using the catalyst according to the invention.

An ethylene polymerization catalyst was prepared as follows.

A slurry of 15.2 grams of "952" silica which had been dried at 200°C was prepared in pentane. The slurry was mixed with 0.26 grams of chromocene. Immediately thereafter, 4.6 grams of tetraisopropyl titanate were mixed into the sieving. Pentane was removed by evaporation. After a brief heating under nitrogen to remove traces of pentane, the residue was activated in an oxygen stream at 780°C for 16 hours. This activated residue was used as a polymerization catalyst using the same procedure <p>g the same equipment as in control A to polymerize ethylene, again using hexane as diluent. A polymerization temperature of 90°C was used under a total pressure of 14 kg/cm 2 gauge pressure for 1 hour. 3 polymerizations were carried out which gave polyethylenes with flow indices of 11.9, 4.8 and 3.6.

The experimental data given above show that when there are variations in the flow index within a series of replicate polymerizations, the catalyst according to the present invention gives significantly higher flow indices than those produced according to the known technique, which is due to differences in the order of addition of the catalyst components and also heat activation steps, both sharing things that provide different ethylene polymerization catalysts.

Claims (8)

Patent requirements. v 1. Ethylene homo- and copolymerization catalysts containing chromium and titanium, optionally also fluorine, on a carrier which consists of an inorganic oxide which (a) has a high surface area and (b) ex selected from aluminum oxide, thorium oxide, silicon oxide, zirconium oxide and mixtures thereof, and (c) is dried at a temperature of 100-800°C, characterized in that it is prepared by the following steps: (1) slurrying dried carrier with a substantially water-free liquid hydrocarbon; (2) mixing the slurry obtained in step (1) with a solution of a chromocene compound of formula wherein each of Y and Y<1> is a hydrocarbon residue of 1-20 carbon atoms and each of n and n<1> has a value of 0 - 5 in a liquid hydrocarbon and a titanium compound which is soluble in hydrocarbon and is calcinable to TiO 2 , whereby the resulting mixture apart from hydrocarbon contains 0.0 2 to 3.0 wt% elemental chromium and 1.0 to 10 wt% elemental titanium; (3) removal of the hydrocarbon to obtain a solid residue;-. (4) heating the product of step (3) in a substantially anhydrous oxygen-containing atmosphere at a temperature of 300 to 1000°C until an active catalyst is obtained. 2. Catalyst according to claim 1, characterized in that up to 5% by weight of a fluorinating agent, calculated as F, is added to the residue from step (3) before step (4). 3. Process for the production of a catalyst according to claim 1, containing chromium and titanium and optionally fluorine on a carrier which is constituted by an inorganic oxide which (a) has a high surface area (b) is selected from aluminum oxide, thorium oxide, silicon dioxide, zirconium oxide and mixtures thereof, and (c) is dried at a temperature of 100-800°C, characterized by the following steps: (1) slurrying dried carrier with a substantially anhydrous liquid hydrocarbon; (2) mixing the slurry obtained in step (1) with a solution of a chromocene compound of formula wherein each of Y and Y' is a hydrocarbon residue of 1 to 20 carbon atoms and each of n and n' has a value of 0 to 5 in a liquid hydrocarbon and a titanium compound which is soluble in hydrocarbon and is calcinable to TiO^, whereby the resulting mixture, exclusive of hydrocarbon, contains 0.0 2 to 3.0 wt% elemental chromium and 1.0 to 10 wt% elemental titanium; (3a) removing the hydrocarbon to obtain a solid residue; (3b) optional fluoridation with up to 5% by weight of a fluoridating agent, calculated as F; (4) heating the product from step (3) in a substantially anhydrous oxygen-containing atmosphere at a temperature of 30 0 to 1000°C until an active catalyst is obtained. 4. Process according to claim 3, characterized in that bis(cyclopentadienyl) chromium II is added as a chromocene compound. 5. Method according to claim 3, characterized in that tetraisopropyl titanate is used as titanium compound. 6. Method according to claim 3, characterized in that (NH^)^ SiFg- is added as a fluoridating agent 7. Method according to claim 3, characterized in that the heating in step (4) takes place to a temperature of 300-800°C. 8. Method according to claim 3, characterized in that isopentane is used as hydrocarbon.